1. Field of the Invention
The present invention generally relates to a vehicle on-board unit. More specifically, the present invention relates to a vehicle on-board unit configured to determine a congestion condition of short range wireless communications.
2. Background Information
Recently, vehicles are being equipped with a variety of informational systems such as navigation systems, Sirius and XM satellite radio systems, two-way satellite services, built-in cell phones, DVD players and the like. These systems are sometimes interconnected for increased functionality. Various informational systems have been proposed that use wireless communications between vehicles and between infrastructures, such as roadside units. These wireless communications have a wide range of applications ranging from crash avoidance to entertainment systems. The type of wireless communications to be used depends on the particular application. Some examples of wireless technologies that are currently available include digital cellular systems, Bluetooth systems, wireless LAN systems and dedicated short range communications (DSRC) systems.
Dedicated short range communications (DSRC) is an emerging technology that has been recently investigated for suitability in vehicles for a wide range of applications. DSRC technology will allow vehicles to communicate directly with other vehicles and with roadside units to exchange a wide range of information. In the United States, DSRC technology will use a high frequency radio transmission (5.9 GHz) that offers the potential to effectively support wireless data communications between vehicles, and between vehicles, roadside units and other infrastructure. The important feature of DSRC technology is that the latency time between communications is very low compared to most other technologies that are currently available. Another important feature of DSRC technology is the capability of conducting both point-to-point wireless communications and broadcast wireless messages in a limited broadcast area.
Accordingly, DSRC technology can be used to provide various information between vehicles, such as providing GPS location, vehicle speed and other vehicle Parameter Identifiers (PIDs) including engine speed, engine run time, engine coolant temperature, barometric pressure, etc. When communications are established from one vehicle to other vehicles in close proximity, this information would be communicated between the vehicles to provide the vehicles with a complete understanding of the vehicles in the broadcast area. This information then can be used by the vehicles for both vehicle safety applications and non-safety applications.
In vehicle safety applications, a “Common Message Set” (CMS) would mostly likely be developed in which a prescribed set of vehicle Parameter Identifiers (PIDs) are broadcast by each vehicle to give relevant kinematical and location information such as GPS location/vehicle position, vehicle speed, vehicle dimensions etc. Once a potential safety concern is determined to exist, a warning system in the vehicles would notify the driver of the potential safety concern so that the driver can take the appropriate action.
In order to enable direct communications among vehicles, DSRC technology supports ad hoc operation mode in which the vehicles directly communicate each other within a communication region without the use of an access point. However, in the wireless ad hoc network system, the network performance tends to decrease when there is localized high-usage of data channel. In other words, DSRC network will most likely experience system congestion in a high volume traffic area where the number of vehicles transmitting DSRC signals is high, and thus, the system capability of the DSRC network will decrease in such area.
The system congestion in the wireless ad hoc network is caused by the hidden terminal problem. The hidden terminal problem occurs when two terminals (e.g., first and second vehicles) that are out of range of one another wish to send data to a third terminal (e.g., a third vehicle). Since the first and second vehicles are out of range of one another, the first and second vehicles could not sense the activities of each other. Thus, when the first and second vehicles try to send the data to the third vehicle, it causes frame collision and data is lost. Since the probability of frame collision increases as the number of vehicles transmitting DSRC signals within the communication region increases, localized congestion in DSRC system becomes high as the number of vehicles transmitting DSRC signals within the communication region increases.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved vehicle on-board unit. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.